Can manufacture

ABSTRACT

A can body is formed from a sheet of metal which has a matte coating composition applied to the portion of the sheet which will become the outside surface of a reentrant convex bottom of the can body.

BACKGROUND

Two-piece cans for beer and other pressurized beverages generally have areentrant convex shape for their bottom. This permits the use of thinnermetal while resisting distortion of the can by the pressure of thebeverage.

Coatings are generally used on the inside of beverage cans to preventcorrosion and to protect the flavor of the beverage. Coatings are alsoused on the outside of beverage cans to facilitate decoration andidentification of the can and its contents. However, if the can is madeof adequately corrosion resistant material such as aluminum ortin-plated steel of an appropriate quality, it is generally notnecessary to apply any coatings to the outside of the bottom of the can.

Although it probably is unlikely, some think it conceivable that aconcave can bottom of uncoated shiney metal, especially bright aluminum,could act as a reflector to concentrate the sun's rays and possiblystart a fire in dry grass or underbrush if a used can is discarded bythe roadside or in the woods.

Exterior coatings are generally applied to two-piece cans after the canbody has been formed. If they were applied before forming, they could beabraided or damaged by the can forming process. And it is difficult tospray a matte coating on the bottom of a formed can without oversprayingonto the sides.

SUMMARY OF THE INVENTION

The present invention provides a process for making a cylindrical canbody with one end closed from a sheet of metal by a deformation process,said closed end having a reentrant convex shape, wherein first only thearea of said sheet which will become the outside surface of said closedend is coated with a flexible coating composition which gives a mattefinish, minimizing specular reflectance of light from said area, thenthe can body is formed from said sheet by a deformation process.

Generally two-piece cans are formed by a drawing and ironing processwherein a ram pushes the center of a flat sheet of metal into a femalemold, often involving more than one ram and mold or more than one step.The initial forming steps are known as drawing. The final step or stepsin which the precise can shape is formed is known as ironing. Theironing ram and mold typically will be shaped to form a reentrant convexshape at the bottom of the can.

Such a can is called a two-piece can to distinguish it from athree-piece can. A two-piece can includes a cup-shaped can body and onelid or end piece. A three-piece can includes a cylinder open at bothends and two lids.

Preferably, the coating composition is applied to flat sheet metalbefore any of the deformation is done to form the can body.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a plan view of part of an uncoiled sheet of metal indicatingthe location of can blanks which are to be coated according to theinvention and cut from the sheet.

FIG. 2 is a perspective view of a partially formed cup shape drawn froma blank of FIG. 1.

FIG. 3 is a perspective view of a formed can body drawn and ironed froma blank of FIG. 1.

FIG. 4 is a cross-sectional view along the section line 4--4 in FIG. 3.

DETAILED DESCRIPTION

Suitable coating compositions are known in the art which are quiteflexible and which dry to give matte finishes. By minimizing specularreflectance, any potential for discarded cans to accidentally causefires in dry grass can be minimized. Matte finishes can be obtained bypigmentation, rough surfaces, or combinations thereof, such as by usingthe compositions disclosed herein.

The flexibility of the coating composition permits applying it to flatsheet and subsequently forming the can body. This avoids thedifficulties of applying a paint to the reentrant bottom of a preformedcan body. If the reentrant bottom of a preformed can is painted byspraying, it can be desirable to mask the sides of the can to preventoverspray. It is easier to confine the spray to a desired area of a flatsheet.

The reentrant convex bottom of the can body can have a variety ofshapes. Generally the shapes will include some portions of smoothcurves, although part of the bottom can be flat. The advantages of theinvention are available in a wide variety of applications which will beapparent from the above to those skilled in the art of can making andcoating.

Turning now to the drawing, FIG. 1 illustrates a portion of an uncoiledsheet 1 of metal, such as thin aluminum or steel, showing the placementof can blanks 2 to be punched from the metal and the location of thematte finish 3 of the invention on the blanks 2. The matte finish 3 canbe coated onto the can blanks 2 before or after they are cut from sheet1 but preferably before.

FIG. 2 is a perspective view of a can blank which has been partiallyformed by drawing a flat blank 2 into a cup shape. FIG. 2 illustratesvertical wall 4 and flat bottom 5 with the matte finish 3 in the middleof flat bottom 5. The partially formed can body is inverted in FIG. 2with open end 6 shown at the bottom. Normally, open end 6 is consideredto be the top of the can. FIG. 3 is a perspective view of a formed canbody drawn and ironed from the partially formed blank of FIG. 2. Theside wall 7 has been lengthened and flat bottom 5 has been decreased indiameter to produce angular shoulder 8 and reentrant convex shape 9.This convex shape 9 is the part of the can which is coated with mattefinish 3.

FIG. 4 is a cross-sectional view taken along cut plane 4--4 of FIG. 3.FIG. 4 more completely illustrates the nature and relationship of convexshape 9 with its matte finish 3 to angular shoulder 8, wall 7 and openend 6.

Of course, the precise contour of a convex shape 9 and the use ofangular shoulder 8 are matters of choice. Other contours, shapes anddesigns can be used in the spirit of the invention.

In the following Example, parts, percentages and proportions are byweight except as indicated otherwise.

EXAMPLE

Acrylic Resin A is prepared, then mixed with the other ingredients asindicated below to make a Can Coating Composition. A Wax Dispersioncombined with an Antiblocking Agent is added as a lubricant for canforming, and the gloss level is adjusted as desired by additions of theGloss Adjusting Clear. The Can Coating Composition is a low gloss blendof an acrylic resin, an epoxy resin and a melamine cross linker.

    ______________________________________                                        Acrylic Resin A                                                               Solvesso 100 hydrocarbon                                                                              14.88                                                 solvent-Exxon                                                                 Ethylene glycol mono-   9.54                                                  ethylether acetate                                                            n-butanol               5.42                                                  Isopropanol             0.96                                                  Add in order - heat to reflux 118° C.                                  Methylmethacrylate      18.72                                                 Ethylacrylate           27.36                                                 Methacrylic acid        1.92                                                  Di-tert butyl peroxide  0.78                                                  Load in premix tank.                                                          Add to reactor over 2 hours period.                                           Hold at reflux for 3 hours.                                                   Solvesso 100            10.60                                                 Ethylene glycol mono-   10.60                                                 butylether                                                                    Total                   100.780                                               Loss                    0.780                                                 Yield                   100.00                                                MMA/EA/MAA weight ratio                                                                           = 39/57/4                                                 Solids by weight    48% (90 min. at 150° C.)                           Acid number         25-30                                                     Viscosity           Z2-Z4 (Gardner Holdt)                                     Liter weight        995 g                                                     Anti-blocking Solution                                                        Acrylic Resin A         16.84                                                 Solvesso 100            29.90                                                 Syloid 74 silica pigment -                                                                            18.48                                                 W. R. Grace                                                                   Ethylene glycol mono-   31.84                                                 butylether                                                                    Solvesso 100            2.94                                                  Grind in sand mill to fineness of <1 μm                                                            100.00                                                particle size.                                                                Adjust solids with 50/50 ethylene glycol                                      mono-butylether and Solvesso 100. -                                                   Solids by weight    26.563%                                           Liter weight            1005 g                                                Fineness                <1 μm                                              Wax Dispersion                                                                Solvesso 150 hydrocarbon                                                                              40                                                    solvent-Exxon                                                                 Polyethylene wax        10                                                    AC 405-Allied Chemical                                                        Heat to 100° C. and mix about 30 min. -Solvesso 150                                            50                                                    Add as fast as possible with rapid                                                                    100                                                   agitation and mix until temperature is                                        below 30° C.                                                           solids by weight    10%                                                       Liter weight        884 g                                                     Gloss Adjustment Clear                                                        Acrylic Resin A         84.96                                                 Epikote 828 epoxy       3.73                                                  resin-Shell Chemical                                                          Cymel 303 highly        2.54                                                  methylated melamine                                                           Ethylene glycol mono-   2.00                                                  butylether                                                                    Solvesso 100            2.00                                                  Wax Dispersion          1.85                                                  Mix 1 hour.                                                                   Ethylene glycol mono-   1.46                                                  butylether                                                                    Soya bean oil           1.46                                                                          100.00                                                Solids by weight    48.7%                                                     Density             0.9943                                                    Can Coating Composition                                                       Acrylic Resin A         65.85                                                 Epikote 828             2.89                                                  Cymel 303               1.97                                                  Ethylene glycol mono-   4.00                                                  butylether                                                                    Solvesso 100            4.00                                                  Add in order with mixing.                                                     Antiblocking Solution   15.600                                                Wax dispersion          1.40                                                  Mix 1 hour - sample to lab for gloss                                          adjustment.                                                                   Anti-blocking solution  trace                                                 Gloss Adjustment Clear  trace                                                 Solvesso 100            2.130                                                 Ethylene glycol mono-   2.130                                                 butylether                                                                                            100.00                                                Solids by weight    40.7%                                                     Gardner Color       2 max                                                     Gardner Gloss       80 min at 85° angle                                Viscosity           DIN 4 85-95                                               Liter weight        985.9 g                                                   Solids by volume    33.400%                                                   Solids Proportions                                                            Resins                                                                        Cymel 303           1.970   5.22                                              Epikote 828         2.890   7.66                                              Acrylic Resin A     32.868  87.12                                                                         100.00                                            Pigment                                                                       Flatting agent     Syloid 74                                                                              2.88                                              ______________________________________                                    

I claim:
 1. A process for making a cylindrical can body with one endclosed from a sheet of metal by a deformation process, said closed endhaving a reentrant convex shape, whereinfirst only the area of saidsheet which will become the outside surface of said closed end is coatedwith a flexible coating composition which gives a matte finish,minimizing specular reflectance of light from said area, then the canbody is formed from said sheet by a deformation process.
 2. The processof claim 1 wherein the deformation process is a drawing and ironingprocess.
 3. The process of claim 1 wherein said sheet is flat when it iscoated, and then the can is formed by a drawing and ironing processwhich also forms the reentrant convex shape.